It is known to produce film capacitors by providing a plastic backing film with a metal coating on one side or both sides. Aluminum or its alloys can be used as a suitable metal. The metal is preferably vaporized by deposition on the backing film. The obtained metal-coated plastic film is used as a starting material in order to press several film portions one upon the other for the production of a package. The several film portions are thereby bonded to one another so that a unitary capacitor package is obtained. The steps which are necessary for the production of the electrode terminals are not mentioned in detail here since they are of no importance for the invention described in the following.
Because of the vaporized metal layers such capacitors have only a limited moisture resistance. Corrosion problems arise since moisture enters betweens the vaporized metal layer and the plastic backing film. Accordingly, although these capacitors are relatively inexpensive to produce, they have, however, only a limited durability.
Such capacitors are encapsulated for improving the moisture resistance. This has the disadvantage that these capacitors cannot be used as chips in the surface installation on account of geometrical reasons. Moreover, such capacitors have only a limited adaptability to necessary soldering methods.
In order to increase the moisture resistance of such film capacitors the Japanese disclosure letter (Kokai) 6-20868 provides the plastic backing film with a coating on water basis in the form of an aqueous solution or an aqueous dispersion. The extruded plastic backing film is longitudinally stretched. Then one side or both sides of the film are either successively or continuously provided with water-based coating in the form of an aqueous solution or an aqueous dispersion. Thereafter, a heat treatment is carried out. Finally, the coating is dried simultaneously with stretching of the film in a traverse direction. Thereafter, the product is subjected to a heat treatment at temperatures of 230.degree. C. A surface-modified plastic film is generated which has a total thickness of 1.0-15 .mu.m, wherein the coating on one side has a thickness of 0.03-0.3 .mu.m.
Then the surface-modified starting film produced in this manner is provided with a metal coating on one side or on both sides in the customary manner. Then the metal-coated films are pressed for the generation of capacitor packages.
Capacitors produced from such films have a better resistance to moisture than capacitors produced from backing films which have not been treated.